1. Field of the Invention
The present invention relates to a receiving apparatus for radio communication system using TDMA (Time Division Multiple Access) method, especially, a control for receiving a control channel at a specific period during a packet data communication.
This is a counterpart of Japanese patent application Serial Number 030108/2007, filed on Feb. 9, 2007, the subject matter of which is incorporated herein by reference.
2. Description of the Related Art
In the simplified mobile phone system referred to as “PHS (Personal Handyphone System), sending and receiving the packet data having one frame of 5 ms by TDMA method using the service channel (communication channel) designated at every linkup between the base and mobile stations. In addition, from the base station, the annunciation signal of radio channel information (hereinafter referred to as only “annunciation signal”) is sent at the interval of the N (for example, N=20) frame period (hereinafter referred to as “LCCH period”) using the dedicated logic control channel (hereinafter referred to as “LCCH”).
In the following patent document 1, the receiving circuit being able to receive the annunciation signal by LCCH during the packet communication (hereinafter referred to as “LCCH steal receiving”) is disclosed.
FIG. 2 is a view of timing diagram of setting the LCCH steal receiving during the packet communication in the conventional receiving circuit described in the patent document 1.
As shown in FIG. 2, in the case where the LCCH receiving is done during the packet data receiving, it is necessary to switch the frequency from the service channel to the LCCH and to switch the expected value of the synchronous pattern referred to as “unique word” (hereinafter referred to as “UW”). Therefore, in order to receive the annunciation information CCH at the interval of the LCCH period during receiving the packet data TCH at 5 ms interval, the LCCH steal counter is installed and counted by the software.
When the value of the LCCH steal counter becomes N−1, the receiving frequency and the UW expected value are switched to ones corresponding to the LCCH in order to receive the LCCH from the following frame. Subsequently, when the UW of the LCCH is detected at the frame starting from the time T1 of FIG. 2, the value of the LCCH steal counter is cleared to zero.
In order to receive the service channel after the following 5 ms, the receiving frequency and the UW expected value are switched to ones corresponding to the service channel Subsequently, when the UW of service channel at the following frame starting from the time T2 is detected, the counter value of the LCCH steal counter is incremented to one. After the above operation, the value of the LCCH steal counter is incremented one by one every time the UW of the service channel is detected.
Subsequently, when the value of the LCCH steal counter becomes N−1, in order to receive the LCCH at the frame starting from the time T3 again, the receiving frequency and the UW expected value are switched to ones corresponding to the LCCH. There is a description that communication data can be received by the above-mentioned operations, using the period while the annunciation signal is received by the LCCH.    Patent document 1: Japanese Patent Number 3793724.